Transmission of control information using more than one beam pair link

ABSTRACT

One way to increase robustness against beam pair link failure is by transmitting downlink (DL) control signaling (e.g., PDCCH) in more than one beam. That is, one way to mitigate BPLF is for the UE to receive DL control signaling over both a first BPL (e.g., active BPL) and a second BPL (e.g., monitored BPL) but with larger duty cycle for the second BPL compared to the first BPL. For example, the control signaling can be scheduled every slot on the first BPL and scheduled every Nth slot on the second BPL. In this way, in case the first BPL is blocked and the UE cannot decode the control signaling on the first BPL, the UE can receive control signaling transmitted on the second BPL.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a 35 U.S.C. § 371 National Stage of InternationalPatent Application No. PCT/EP2017/078193, filed Nov. 3, 2017,designating the United States and claiming priority to U.S. provisionalapplication No. 62/417,633, filed on Nov. 4, 2016. The above identifiedapplications are incorporated by reference.

TECHNICAL FIELD

Disclosed are embodiments for transmitting control information to a UEusing more than one (i.e., a plurality of) beam pair links (BPLs).

BACKGROUND

1.0 Introduction

The Third Generation Partnership Project (3GPP) has begun on work on thedevelopment and design of the next generation mobile communicationssystem (a.k.a., as the 5G mobile communication system or simply “5G” forshort). 5G will encompass an evolution of today's 4G networks and theaddition of a new, globally standardized radio access technology knownas “New Radio” (NR).

The large variety of requirements for NR implies that frequency bands atmany different carrier frequencies will be needed. For example, lowbands will be needed to achieve sufficient coverage and higher bands(e.g. mmW, such as near and above 30 GHz) will be needed to reach therequired capacity. At high frequencies the propagation properties aremore challenging and high order beamforming at the base station (e.g.,eNB or gNB) will be required to reach sufficient link budget. Forexample, narrow beam transmission and reception schemes may be needed athigher frequencies to compensate the high propagation loss. For a givencommunication link, a beam can be applied at the transmission point,TRP, (i.e., a transmit (TX) beam) and a beam can be applied at the userequipment (UE) (i.e., a receive (RX) beam)), which collectively isreferred to as a “beam pair link” (BPL) or just “link” for short.

NR will have a beam centric design, which means that the traditionalcell concept is relaxed and user equipments (UEs) (i.e., fixed or mobilewireless communication devices) will in many cases be connected to andperform “handover” between narrow beams instead of cells. Hence, 3GPPhas agreed to study concepts for handling mobility between beams (bothwithin and between transmission points (TRPs)). As used herein, a TRP isa base station or a component of a base station. At higher frequencies,where high-gain beamforming will be needed, each beam will be usefulonly within a small area (i.e., the beam's coverage area) and the linkbudget outside the coverage area will deteriorate quickly. Hence, afrequent and fast beam switching method is needed to maintain highperformance.

1.1 Beamforming

Beamforming implies transmitting the same signal from multiple antennaelements of an antenna array with an amplitude and/or phase shiftapplied to the signal for each antenna elements. These amplitude/phaseshifts are commonly denoted as the antenna weights and the collection ofthe antenna weights for each of the antennas is a precoding vector. Suchantenna weights and precoding vectors are examples of a transmit spatialfiltering configuration.

Different transmit spatial filtering configurations (e.g., differentprecoding vectors) give rise to a beamforming of the transmitted signaland the weights can be controlled so that the signals are coherentlycombining in a certain angle direction as seen from the antenna array inwhich case it is said that a transmit (TX) beam is formed in thatdirection. Hence, in some contexts, when we refer to a TX beam we arereferring to a particular transmit spatial filtering configuration(a.k.a., “beamforming weights” or “beam parameters”), and when we referto an RX beam we are referring to a particular receive spatial filteringconfiguration. If the antennas of the array are placed in twodimensions, i.e. in a plane, then the beam can be steered in bothazimuth and elevation directions with respect to the plane perpendicularto the antenna array.

1.2 Reference Signals, Antenna Ports and Quasi Co-Location (QCL)

In LTE, reference signals (RSs) used for channel estimation areequivalently denoted as antenna ports. Hence a UE can estimate thechannel from one antenna port by using the associated RS. One could thenassociate a certain data or control transmission with an antenna port,which is equivalent to say that the UE shall use the RS for that antennaport to estimate the channel used to demodulate the associated controlor data channel. One could also say that the data or control channel istransmitted using that antenna port.

In LTE, the concept of quasi-co location has been introduced in order toimprove the channel estimation performance when demodulating control ordata channels. The concept relies on that the UE could estimate longterm channel properties from one reference signal in order to tune itschannel estimation algorithm. For instance, the average channel delayspread can be estimated using one antenna port and used whendemodulating a data channel transmitted using another antenna port. Ifthis is allowed, it is specified that the first and second antenna portare quasi co-located (QCL) w.r.t average channel delay spread.

Hence, as used in LTE specifications, two antenna ports are “quasico-located” if the large-scale channel properties of the channel overwhich a symbol on one antenna port is conveyed can be inferred from thechannel over which a symbol on the other antenna port is conveyed. Thelarge-scale channel properties preferably include one or more of delayspread, Doppler spread, Doppler shift, average gain, and average delay.

In addition, or alternatively, the large-scale channel properties caninclude one or more of received power for each port, received timing(i.e., timing of a first significant channel tap), a number ofsignificant channel taps, and frequency shift. By performing channelestimation algorithm tuning based on the RSs corresponding to the quasico-located antenna ports, a quality of the channel estimation issubstantially improved.

In NR, it has been agreed to introduce QCL for spatial properties of thechannel on top of those QCL parameters use for LTE. By complementing theexisting QCL framework with new QCL parameters that depends on spatialchannel properties, we can allow a UE to perform spatial processingacross different signal types without violating the rule that a UE isnot allowed to use measurements from one reference signal to assist inthe reception or processing of another signal unless explicitlyspecified.

Examples of such spatial processing is analog receiver beamforming, andchannel estimation using spatial processing gain to improve the channelestimate.

Assume communication between two nodes in a network, a TX node and an RXnode. A TX node transmits a first set of reference signals (RS) from oneor multiple transmit antenna ports. An RX node receives the transmittedreference signals using one or multiple receive antenna ports anddetermines or estimates, based on the received first set of transmittedRS, one or more parameters capturing a spatial property of the channel.The RX node determines an indication that a second set of transmitted RSfrom one or multiple transmit antenna ports are quasi co-located (QCL)with the first RS, where the QCL is given with respect to the one ormore parameters capturing a spatial property of the channel. The TX nodetransmits the second set of transmit RS from one or multiple transmitantenna ports. The RX node utilizes one or more of the determinedparameters capturing a spatial property of the channel that is based onthe first set of RS, to assist in the reception of the second set of RS.

In other words, the RX node, typically a UE can use the same RXbeamforming weights to receive the second signals and associated RS(such as a control or a data transmission DMRS) as the RX beamformingweights it used when it received a first signal (for example ameasurement signal, e.g. CSI-RS) if the second RS is QCL with the firstRS with respect to spatial parameters.

A QCL parameter related to a spatial property is related to the UE RXbeamforming or UE RX reception parameters. Hence, if the UE use twodifferent spatial QCL parameters can indicate that the UE use twodifferent RX beamforming weights (or equivalently two different ways ofcombining the signals from the UE RX antennas).

Spatial parameters could be angle of arrival, angular spread or spatialcorrelation, spatial correlation matrix on the RX side or on the TXside.

It has been agreed for NR that information pertaining to UE-sidebeamforming/receiving procedure used for data reception can be indicatedthrough QCL to UE (from the base station).

1.3 Control Channel Search Space and Control Signaling

Information transmitted over the radio link to users can be broadlyclassified as control information (a.k.a., control messages) or userdata. Control information is used to facilitate the proper operation ofthe system as well as the proper operation of each UE within the system.Control information could include commands to control functions such asthe transmitted power from a UE, signaling of resource blocks (RBs)within which information is to be received by the UE or transmitted fromthe UE and so on. Examples of control information include a physicaldownlink control channel (PDCCH) which for example carries schedulinginformation and power control messages, a physical HARQ indicatorchannel (PHICH) that carries ACK/NACK messages sent in response to aprevious uplink transmission, and a physical broadcast channel (PBCH)that carries system information. Also the primary and secondarysynchronization signals (PSS/SSS) can be seen as control signals withfixed locations and periodicity in time and frequency so that UEs thatinitially access the network can find them and synchronize.

The PBCH in LTE is not scheduled by a PDCCH transmission but has a fixedlocation relative to the primary and secondary synchronization signals(PSS/SSS). Therefore, the LTE UE can receive the system informationtransmitted in BCH before it is able to read the PDCCH. It shall benoted that payload in BCH (which is referred to as the masterinformation block (MIB)) is not fully utilized but contains someunassigned “spare” bits which can be used for future use.

In LTE Rel-10, all control messages to UEs are demodulated using a cellspecific RS (CRS) hence they have a cell wide coverage to reach all UEsin the cell without having knowledge about their position. An exceptionis the PSS and SSS which are stand-alone and do not need reception ofCRS before demodulation. The first one to four OFDM symbols, dependingon the configuration, in a subframe are reserved to contain such controlinformation, as shown in FIG. 1. Control messages could be categorizedinto those types of messages that need to be sent only to one UE(UE-specific control) and those that need to be sent to all UEs or somesubset of UEs numbering more than one (common control) within the cellbeing covered by the eNB.

Control messages of PDCCH type are demodulated using CRS and transmittedin multiples of units called control channel elements (CCEs) where eachCCE contains 36 resource elements (REs). A PDCCH may have aggregationlevel (AL) of 1, 2, 4 or 8 CCEs to allow for link adaptation of thecontrol message. Furthermore, each CCE is mapped to 9 resource elementgroups (REG) consisting of 4 REs each. These REGs are distributed overthe whole system bandwidth to provide frequency diversity for a CCE.Hence, the PDCCH, which consists of up to 8 CCEs spans the entire systembandwidth in the first one to four OFDM symbols, depending on theconfiguration.

Transmission of the physical downlink shared data channel (PDSCH) to LTEUEs, is using the RE in a RB pair that are not used for control messages(i.e., in the data area of shown in FIG. 1) or RS and can either betransmitted using the UE specific RS or the CRS as a demodulationreference, depending on the PDSCH transmission mode. The use ofUE-specific RS in LTE allows a multi-antenna LTE base station (eNB) tooptimize the transmission using pre-coding of both data and referencesignals being transmitted from the multiple antennas so that thereceived signal energy increase at the UE and consequently, the channelestimation performance is improved and the data rate of the transmissioncould be increased.

For NR, it is foreseen that UE specific RS is used for control channeltransmissions as well.

1.3.1 PDCCH Processing in LTE

After channel coding, scrambling, modulation and interleaving of thecontrol information the modulated symbols are mapped to the resourceelements in the control area. As mentioned above, control channelelements (CCE) have been defined, where each CCE maps to 36 resourceelements. By choosing the aggregation level, link-adaptation of thePDCCH obtained. In total there are NCCE CCEs available for all the PDCCHto be transmitted in the subframe and the number NCCE varies fromsubframe to subframe depending on the number of control symbols n andthe number of configured PHICH resources.

As NCCE varies from subframe to subframe, the terminal would need toblindly determine the position as well as the number of CCEs used forits PDCCH which can be a computationally intensive decoding task.Therefore, some restrictions in the number of possible blind decodings aterminal needs to go through have been introduced in Rel.8. Forinstance, the CCEs are numbered and CCE aggregation levels of size K canonly start on CCE numbers evenly divisible by K, see FIG. 2.

The set of CCE where a terminal needs to blindly decode and search for avalid PDCCH is called the UEs “search space.” This is the set of CCEs ona AL a terminal should monitor for scheduling assignments or othercontrol information, see example in FIG. 3. In each subframe and on eachAL, a terminal will attempt to decode all the PDCCHs that can be formedfrom the CCEs in its search space. If the CRC checks, then the contentof the PDCCH is assumed to be valid for the terminal and it furtherprocesses the received information. Often will two or more terminalshave overlapping search spaces and the network has to select one of themfor scheduling of the control channel. When this happens, thenon-scheduled terminal is to be blocked. The search spaces for a UE varypseudo-randomly from subframe to subframe to minimize this blockingprobability.

A search space is further divided to a common and a terminal specificpart. In the common search space, the PDCCH containing information toall or a group of terminals is transmitted (paging, system information,etc.). If carrier aggregation is used, a terminal will find the commonsearch space present on the primary component carrier (PCC) only. Thecommon search space is restricted to aggregation levels 4 and 8 to givesufficient channel code protection for all terminals in the cell (sinceit is a broadcast channel, link adaptation cannot be used). The m8 andm4 first PDCCH (first in the meaning of having with lowest CCE number)in an AL of 8 or 4 respectively belongs to the common search space. Forefficient use of the CCEs in the system, the remaining search space isterminal specific at each aggregation level.

A CCE consist of 36 QPSK modulated symbols that map to the 36 RE uniquefor this CCE. Hence, knowing the CCE means that also the RE is knownautomatically. To maximize the diversity and interference randomization,interleaving is used before a cell specific cyclic shift and mapping toREs, see the processing steps in FIG. 4. Note that in most cases aresome CCEs empty due to the PDCCH location restriction to terminal searchspaces and aggregation levels. The empty CCEs are included in theinterleaving process and mapping to RE as any other PDCCH to maintainthe search space structure. Empty CCE are set to zero power and thispower can instead be used by non-empty CCEs to further enhance the PDCCHtransmission.

Furthermore, to enable the use of 4 antenna TX diversity, a group of 4adjacent QPSK symbols in a CCE is mapped to 4 adjacent RE, denoted a REgroup (REG). Hence, the CCE interleaving is quadruplex (group of 4)based and mapping process has a granularity of 1 REG and one CCEcorresponds to 9 REGs (=36 RE).

In LTE, each PDCCH is mapped to RE in all OFDM symbols configured forthe control area. This is also seen in FIG. 1 mapping of one CCEbelonging to a PDCCH in LTE to the control area which spans the wholesystem bandwidth.

SUMMARY

One problem with connecting UEs to a narrow beam is that the signaltransmitted on the beam could easily be deteriorated for example if anobject gets in the way of the beamformed signal and blocks it. Due tohigh penetration loss and poor diffraction properties at highfrequencies a blocking object can lead to lost connection between the TXbeam and UE so that the control channel cannot be decoded, which mightlead to dropped calls and bad user experience. Such a scenario would beconsidered a “beam pair link failure” (BPLF).

It is thus a problem how to maintain a communication link with the UEeven in operating conditions of narrow beams and presence of blockingobjects. In particular it is a problem how to transmit and receivedownlink (DL) control signaling (e.g., PDCCH) carrying data schedulingassignments or scheduling grants in such operating conditions.

One way to overcome this problem is to increase robustness against beampair link failure by transmitting DL control signaling (e.g., PDCCH) inmore than one beam (i.e., transmit DL control signaling using more thanone transmit spatial filtering configuration). That is, one way tomitigate BPLF is for the UE to receive DL control signaling over both afirst BPL (sometimes called the “active link”) and a second BPL(sometimes called the monitored link) but with larger duty cycle for thesecond BPL compared to the first BPL. For example, the control signalingcan be scheduled every slot on the first link and scheduled every N^(th)slot on the second link. In this way, in case the first BPL is blockedand the UE cannot decode the control signaling on the first BPL (i.e.,the control signaling transmitted using a first transmit spatialconfiguration), the UE can receive control signaling transmitted on thesecond link (i.e., the control signaling transmitted using a secondtransmit spatial configuration).

Preferably, the transmission of the control signaling on more than oneBPL is performed in an efficient way. Additionally, the UEs should beconfigured to monitor the BPLs in a robust and efficient manner. A mainadvantage of doing this is that the connection, particularly the PDCCHtransmission and reception at high frequencies, will be more robust withrespect to BPLFs.

Transmitting control signaling in more than one beam can beaccomplished, in one embodiment, by having each control channelcandidate in the control channel search space be associated with aspatial QCL parameter. In other words, two control channel candidatescan be received with different UE RX beams and thus two different TXbeams respectively if the two candidates have different QCL parameterswith respect to spatial properties. This gives robustness against beampair link failure as both an active and a monitored BPL can be used toschedule data messages to or from the UE.

Hence, in addition to the TRP transmitting the PDCCH to a UE using anfirst BPL (e.g., active BPL), and hence using a first TX beam (e.g.,using an first precoding vector), for the UE, the TRP transmits thePDCCH to the UE using a second BPL (e.g., monitored BPL), and henceusing a second TX beam (e.g., using a second precoding vector), toachieve diversity. In some embodiments, a longer duty cycle is used forthe PDCCH transmitted using the second BPL compared to the first BPL.The relation between the spatial QCL parameter and the PDCCH candidateto use when attempting to decode the PDCCH can be different fordifferent PDCCH candidates in the search space in one subframe or indifferent subframes (or other defined time periods). Alternatively, theassociation between a PDCCH candidate and the used TX beam and thus theRX beam to use when attempting to decode the PDCCH can be different fordifferent PDCCH candidates in the search space for the UE, either in onesubframe or in different subframes (or equivalently in other definedtime periods).

Accordingly, in one aspect there is provided a method performed by a TRPfor communicating with a UE. The method includes: using a first beampair link, BPL for communicating with the UE, wherein the first BPLcomprises a first transmit spatial filtering configuration and a firstreceive spatial filtering configuration corresponding to the firsttransmit spatial filtering configuration, transmitting controlinformation to the UE using the first BPL, and providing to the UEscheduling information indicating a slot in which the TRP may transmitcontrol information to the UE using a second BPL, wherein the second BPLcomprises a second transmit spatial filtering configuration.

In some embodiments the method further includes: the TRP detecting thatthe first BPL has experienced a beam pair link failure, BPLF, and, as aresult of detecting that the first BPL has experienced a BPLF, the TRPtransmitting control information to the UE in the indicated slot usingthe second BPL.

In some embodiments, the control information transmitted to the UE inthe indicated slot using the second BPL informs the UE that the secondBPL is now an active BPL for the UE. In some embodiments, the UE isconfigured such that the UE will search a control area of the indicatedslot for control information transmitted by the TRP using the secondBPL.

In some embodiments the step of transmitting control information to theUE using the first BPL comprises transmitting control information to theUE using the first BPL in not more than M of N consecutive slots,wherein N is greater than 1 and M is less than or equal to N, and theindicated slot is one of the N consecutive slots. In some embodimentsthe scheduling information indicates L slots in which the TRP maytransmit control information to the UE using the second BPL, wherein Lis greater than or equal to 1 and L is less than M, and each of the Lslots is one of the N consecutive slots. In some embodiments M=N−1 andL=1. In some embodiments in one of the N consecutive slots the TRPtransmits control information to the UE using the second BPL but doesnot transmit control information to the UE using the first BPL. In someembodiments M=N and L=1.

In another aspect there is a method performed by one or more TRPscommunicating with a UE. The method includes: defining a first searchspace and a second search space, wherein a first transmit spatialfiltering configuration is associated with the first search space and asecond transmit spatial filtering configuration is associated with thesecond search space, for a transmission of a control channel candidateto the UE, selecting the first or second search space, and transmittingthe control channel candidate in control channel resources belonging tothe selected search space using the transmit spatial filteringconfiguration associated with the selected search space.

In some embodiments the first transmit spatial filtering configurationis related to a first BPL and the second transmit spatial filteringconfiguration is related to a second BPL. In some embodiments theselection is based on information that the first BPL has experienced abeam pair link failure (BPLF).

In some embodiments the first search space is a first portion of acontrol area, and the second search space is a second portion of thecontrol area. In some embodiments the first portion of the control areaand the second portion of the control area overlap in time at leastpartially, or the first portion of the control area does not overlap intime with the second portion of the control area.

In some embodiments the first search space is a first control area, andthe second search space is a second control area. In some embodimentsthe first control area and the second control area overlap in time atleast partially, or the first control area does not overlap in time withthe second control area.

In another aspect there is provided a TRP that is configured to performany of the TRP methods described in this disclosure. For example, insome embodiments, the TRP includes a transmitter, a receiver, a memory,and a data processing system comprising one or more processors, whereinthe TRP is configured to perform any of the TRP methods described inthis disclosure.

In another aspect there is provided a method performed by a UEcommunicating with one or more TRPs, wherein the TRPs are configured totransmit information to the UE using a first beam pair link, BPL,comprising a first transmit spatial filtering configuration and a firstreceive spatial filtering configuration corresponding to the firsttransmit spatial filtering configuration. The method includes the UEusing the first receive spatial filtering configuration corresponding tothe first transmit spatial filtering configuration to obtain controlinformation transmitted to the UE using the first BPL, and the UEobtaining scheduling information indicating a slot in which one of theTRPs may transmit control information to the UE using a second BPLcomprising a second transmit spatial filtering configuration and asecond receive spatial filtering configuration corresponding to thesecond transmit spatial filtering configuration.

In some embodiments a TRP transmits in the slot the control informationto the UE using the second BPL in the event that the TRP detects thatthe first BPL has experienced a beam pair link failure.

In some embodiments, as a result of receiving the schedulinginformation, the UE uses the second receive spatial filteringconfiguration corresponding to the second transmit spatial filteringconfiguration to search the indicated slot for control informationtransmitted to the UE, and, as a result of the search, the UE obtainscontrol information transmitted to the UE, and the obtained controlinformation informs the UE that he second BPL is now an active BPL forthe UE.

In some embodiments the indicated slot is a slot in which a TRP does nottransmit control information to the UE using the first BPL.

In another aspect there is another method performed by the UE. Themethod includes: the UE using a first parameter corresponding to a firstBPL to search a first search space for control information transmittedby a TRP to the UE using the first BPL, and the UE using a secondparameter corresponding to a second BPL to search a second search spacefor control information transmitted by a TRP to the UE using the secondBPL. The first BPL comprises a first transmit spatial filteringconfiguration and a first receive spatial filtering configurationcorresponding to the first transmit spatial filtering configuration. Thesecond BPL comprises a second transmit spatial filtering configurationand a second receive spatial filtering configuration corresponding tothe second transmit spatial filtering configuration. In someembodiments, the UE uses the second parameter corresponding to thesecond BPL to search the second search space for control informationwhen the UE is unable to find the control information transmitted usingthe first BPL.

In another aspect there is another method performed by the UE. Themethod includes: the UE using a first QCL parameter for receiving acontrol channel candidate transmitted in a first search space, and theUE using a second QCL parameter for receiving a control channelcandidate transmitted in a second search space. In some embodiments, thefirst search space is a first portion of a control area, and the secondsearch space is a second portion of the control area. In someembodiments, the first portion of the control area and the secondportion of the control area overlap in time at least partially, or thefirst portion of the control area does not overlap in time with thesecond portion of the control area.

In some embodiments, the first search space is a first control area, andthe second search space is a second control area. In some embodiments,the first control area and the second control area overlap in time atleast partially, or the first control area does not overlap in time withthe second control area.

In some embodiments, the method also includes the UE receivingconfiguration information using a higher layer message, wherein theconfiguration information configures first and second search spaces.

In another aspect there is provided a UE that is configured to performany of the UE methods described in this disclosure. For example, in someembodiments, the UE includes a transmitter, a receiver, a memory, and adata processing system comprising one or more processors, wherein the UEis configured to perform any of the UE methods described in thisdisclosure.

In another aspect there is provided a method performed by a systemcomprising a first TRP for communicating with a UE and a second TRP forcommunicating with the UE. The method includes: the first TRP using afirst beam pair link (BPL) for communicating with the UE, the second TRPusing a second BPL for communicating with the UE, the first TRPtransmitting control information to the UE using the first BPL, andproviding to the UE scheduling information indicating a slot in whichthe second TRP may transmit control information to the UE using thesecond BPL.

In some embodiments the method also includes: detecting that the firstBPL has experienced a beam pair link failure (BPLF), as a result ofdetecting that the first BPL has experienced a BPLF, the second TRPtransmitting control information to the UE in the indicated slot usingthe second BPL. In some embodiments the control information transmittedto the UE in the indicated slot using the second BPL informs the UE thatthe second BPL is now an active BPL for the UE. In some embodiments theUE is configured such that the UE will search a control area of theindicated slot for control information transmitted by the second TRPusing the second BPL.

In some embodiments the step of transmitting control information to theUE using the first BPL comprises transmitting control information to theUE using the first BPL in not more than M of N consecutive slots,wherein N is greater than 1 and M is less than or equal to N, and theindicated slot is one of the N consecutive slots. In some embodimentsthe scheduling information indicates L slots in which the second TRP maytransmit control information to the UE using the second BPL, wherein Lis greater than or equal to 1 and L is less than M, and each of the Lslots is one of the N consecutive slots. In some embodiments M=N−1 andL=1. In some embodiments, in one of the N consecutive slots the secondTRP transmits control information to the UE using the second BPL but thefirst TRP does not transmit control information to the UE using thefirst BPL. In some embodiments M=N and L=1.

In another aspect there is provided another method performed by one ormore TRPs. The method includes: a TRP using a first transmit spatialfiltering configuration to transmit a PDCCH control message in a firstsearch space, and a TRP using a second transmit spatial filteringconfiguration to transmit a PDCCH control message in a second searchspace. In some embodiments, the first search space is a first portion ofa control area, and the second search space is a second portion of thecontrol area, or the first search space is a first control area, and thesecond search space is a second control area.

In another aspect there is provided another method performed by one ormore TRPs. The method includes: a TRP using a first transmit spatialfiltering configuration to transmit a PDCCH control message in a firstset of one or more symbols of a slot, a TRP using a second transmitspatial filtering configuration to transmit a PDCCH control message in asecond set of one or more symbols of the slot.

In another aspect there is provided another method performed by a UE.The method includes: the UE using a first receive spatial filteringconfiguration to search for a PDCCH control message in a first searchspace, and the UE using a second receive spatial filtering configurationto search for a PDCCH control message in a second search space. In someembodiments, the first search space is a first portion of a controlarea, and the second search space is a second portion of the controlarea, or the first search space is a first control area, and the secondsearch space is a second control area.

In another aspect there is provided another method performed by a UE.The method includes: the UE using a first receive, receive spatialfiltering configuration to search for a PDCCH control message in a firstset of one or more symbols, and the UE using a second receive spatialfiltering configuration to search for a PDCCH control message in asecond set of one or more symbols.

In another aspect there is a method that includes performing at leastone of: configuring a UE to monitor a PDCCH on M beam pair linkssimultaneously, wherein M is greater than 1, and configuring the UE tomonitor the PDCCH on different beam pair links in different PDCCH OFDMsymbols.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate various embodiments.

FIG. 1 illustrates an exemplary subframe.

FIG. 2 illustrates CCE aggregation.

FIG. 3 illustrates an example search space.

FIG. 4 is a flow chart illustrating processing steps.

FIGS. 5A, 5B and 5C illustrate the use of active and monitored BPLs forcommunications between a TRP and a UE.

FIG. 6 is a flow chart illustrating a process according to oneembodiment.

FIG. 7 is a flow chart illustrating a process according to oneembodiment.

FIG. 8 is a flow chart illustrating a process according to oneembodiment.

FIG. 9 is a flow chart illustrating a process according to oneembodiment.

FIG. 10 is a flow chart illustrating a process according to oneembodiment.

FIG. 11 is a flow chart illustrating a process according to oneembodiment.

FIG. 13 is a block diagram of a UE according to some embodiments.

FIG. 14 is a block diagram of TRP according to some embodiments.

FIG. 15 illustrate the use of first and second BPLs for communicationsbetween two TRPs and a UE.

DETAILED DESCRIPTION

One way to mitigate the problem of BPLF is to use a second (e.g.,monitored (a.k.a., backup)) transmit (TX) beam (e.g., use, among otherthings, a second precoding vector) that can be used in case the first(e.g., active) BPL experiences a BPLF (e.g., is blocked). Hence, atleast two TX beams (e.g., at least two precoding vectors) are used tocommunicate with a UE. In the case the UE preforms receive (RX)beamforming using analog beamformers, the UE can only tune its RX beamto one TX beam at a time. Likewise, if the TRP uses analog beamforming,only one beam can be transmitted at a time. Hence, there is a need toalign the TX beam (i.e., transmit spatial filtering configuration) withthe correct RX beam (i.e., receive spatial filtering configuration) at agiven time. For each TX beam there is an “optimal” UE RX beamcorresponding to the TX beam (e.g., optimal receive spatial filteringconfiguration, which may include phase and/or amplitude adjustmentparameters for each signal received via multiple receive antennas, whichparameters are applied to the signals before combining or summation ofthe signals).

A first transmit spatial filtering configuration (i.e., TX beam) and itscorresponding receive spatial filtering configuration (i.e., RX beam) atthe UE can be seen as a first beam pair link (BPL), which is used forthe control and possibly also the data transmission. In addition, asecondary TX beam (i.e., one or more secondary TX beams) andcorresponding RX beams can be used as secondary (e.g., monitored) BPLs.

Beam management refers to maintaining a beam pair link by, for example,triggering the UE to make measurements and report measurement results.The purpose of the second BPL (hereafter “monitored BPL”) is to 1)discover new BPLs that are better than the first BPL (hereafter “activeBPL”), and 2) have a monitored BPL in case the active BPL experiences aBPLF. Since the majority of the communication takes place using theactive BPL (i.e., the active TX beam and the active RX beam), thesecondary BPLs can be seen as being “backup” or “monitored” BPLs.

An example of this is illustrated in FIGS. 5A, 5B and 5C. In FIG. 5A,there is shown a TRP 550 (e.g., a base station) using one active BPL forUE 501 to transmit to the UE control information (e.g., PDCCH) and userdata and further using one monitored (backup) BPL for the UE. WhileFIGS. 5A, 5B, and 5C illustrate a single TRP communicating with the UE,in other embodiments two or more TRPs may be communicating with the TRP,wherein one of the TRPs uses the active BPL to communicate with the UEand another of the TRPs uses the monitored BPL to communicate with theUE (see e.g., FIG. 15).

The active BPL comprises active transmit (TX) beam 502 and thecorresponding active RX beam 506, and the monitored BPL comprises themonitored TX beam 504 and the corresponding monitored RX beam 508. TheUE is decoding PDCCH candidates in the search space using the RX beam506 corresponding to the active TX beam 502 (i.e., the base station istransmitting its PDCCH to the UE using the active TX beam). PDCCH isused throughout to indicate the control channel carries schedulinginformation. Another term may be NR-PDCCH.

In FIG. 5B there is shown an object 590 that is blocking the active BPL,thereby causing the UE to detect a BPLF with respect to the active BPL(i.e., the active TX beam/active RX beam pair). A problem arises in thatthe TRP cannot switch the PDCCH transmission to the monitored BPL sincethe UE is still monitoring the UE RX beam 506 corresponding to theactive TX beam 502 as the UE is unaware of the blocking. Moreover, theTRP may also be unaware of the blocking situation.

To restore the connection between the TRP and the UE, the TRP can usethe monitored BPL as the active BPL for the UE, as illustrated in FIG.5C. However, to efficiently perform this beam switching, the TRP mustfirst signal to the UE that it will start using the monitored BPL as theactive BPL, otherwise the UE will not know which UE RX beam to useduring reception (i.e., RX beam 506 or RX beam 508). This is problematicbecause the active BPL, which is used for control signaling, is blockedand has poor or non-existing channel quality. If the blocking happensslowly, there may be time to perform this signaling before the signaldegrades too much.

There is a risk that the blocking will happen too quickly such that theTRP does not have time to signal a “beam switch” (a.k.a., “BPL switch”)to the UE, and in this case the UE will continue to search, withoutsuccess, for PDCCH using the RX beam 506 corresponding to the TX beam502 that is now blocked. Embodiments disclosed here overcome thisproblem.

In one embodiment, the TRP transmits the PDCCH (or other controlinformation) to the UE using both an active BPL and a monitored BPL,thereby improving diversity and thus improving robustness. In someembodiments, the fraction of time or resources for which the monitoredBPL is used for PDCCH transmission and reception is controlled, forinstance by higher layer signaling, such as RRC signaling.

Typically, the PDCCH will be transmitted more rarely using the monitoredBPL compared with the active BPL. For example, in one embodiment thePDCCH is time multiplexed between the active and the monitored BPLs suchthat in every Nth subframe (e.g., N is configured by the network) theTRP transmits the PDCCH to the UE using the monitored BPL for the UEinstead of the active BPL for the UE. In another embodiment, the PDCCHis always transmitted to the UE using the active BPL for the UE butevery Nth subframe (e.g., N configured by the network) the PDCCH is alsotransmitted to the UE using the monitored BPL for the UE.

On the UE side, the corresponding embodiments holds in case the UE usesUE RX beamforming: 1) the PDCCH search space is time multiplexed betweenthe active and the monitored BPLs such that in every Nth subframe the UEreceives the PDCCH search space using the monitored BPL instead of theactive BPL; and 2) the PDCCH search space is always monitored using theactive BPL but every Nth subframe the PDCCH is also monitored using themonitored BPL.

In the first embodiment the PDCCH transmission for the given UE is timemultiplexed between the active BPL and the monitored BPL but preferablewith a longer duty cycle for the monitored BPL. Hence, the UE shall usethe RX beam corresponding to the monitored BPL (i.e., the RX beam of themonitored beam pair link) whenever the network is using the monitoredBPL for PDCCH transmission. So the network and UE are synchronized inwhen to use the first or second (i.e. active and monitored) beam pairlink for PDCCH transmission and reception.

For example, the PDCCH is transmitted nine times in a row using theactive BPL and the tenth time using the monitored BPL.

In one embodiment this can be achieved by associating a PDCCH candidatewith a certain spatial correlation or angle of arrival parameter in thequasi-colocation framework in a given subframe. Hence, when receiving aPDCCH candidate, the UE also knows the QCL parameter for that PDCCH, soit knows which RX beam to use for its reception. The PDCCH is thusspatially QCL with a beam management process, with a given identity, ora link identifier (such as active/monitored or [beam pair] link 1, link2 etc) or an RS or another signal. Hence, the PDCCH may alternatively bespatially QCL with the identity or resource of a CSI measurementreference signal that previously has been transmitted. Alternatively,the PDCCH may be spatially QCL with a measurement signal used formobility or synchronization, such as mobility RS, beam RS, primary orsecondary synchronization signals (PSS,SSS).

The TRP signals to the UE which previous signal, RS or process is QCLwith respect to spatial parameter with the demodulation RS used forPDCCH reception. This signaling may be explicit, implicit (includinggiven by a rule in the standard specification).

Hence, PDCCH candidates are QCL with at least two different spatial QCLsettings and the UE may adjust its receive beam depending on the QCLsetting. The active BPL has one spatial QCL setting (a first RX beam)and the monitored BPL a different spatial QCL setting (a second RXbeam). In the first embodiment the PDCCH transmission for the given UEfrom the TRP is time multiplexed between the active BPL and themonitored BPL, and the UE use the spatial QCL settings accordingly, butwith a possible longer duty cycle for the monitored BPL.

The relation between spatial QCL parameter and the PDCCH candidate canbe per subframe. Hence, the spatial QCL parameter to use for receivingPDCCH is at least dependent on a time index, such as subframe.

More generally; a sub-set (or all) of the PDCCH search space candidatesin a given subframe are located in the monitored BPL with a longer dutycycle. In this case, the relation between the spatial QCL parameter andthe PDCCH candidate can be different for different candidates. So theTRP may transmit the PDCCH candidate in different TX beams and the UEuse different UE RX beams to receive and attempt to decode thecandidate. Which RX beam to use is given by the spatial QCL parameterassociated with the PDCCH candidate.

The UE will know the time schedule and hence listen with the correct UERX beam at the right times. FIG. 6 illustrates a method according to anembodiment. In step 602 the TRP defines the first and second (e.g.,active and monitored) BPL (beam tracking processes) and signals this tothe UE. Each beam tracking process may be associated with a spatial QCLparameter. Alternatively, each tracking process is associated with anindex of a previous CSI-RS measurement or a mobility RX (MRS) so the UEknows that the network will use the same beam for the PDCCH as ispreviously used for a CSI-RS or MRS transmission. The TRP also defines atime schedule for how to time multiplex the PDCCH transmissions betweenthe first and second (e.g., active and monitored) BPLs and signals thisinfo to the UE (step 604). In step 606, the TRP transmits the PDCCHusing the first and second (e.g., active and monitored) BPLs accordingto the time schedule. And in step 608, the UE receives the PDCCH usingthe UE RX beam that corresponds to the first and second BPLs. In casethe PDCCH from second BPL is detected but not the PDCCH from the firstBPL, the TRP should switch such that the second BPL becomes the newactive BPL. This could for example be included in the PDCCH signaltransmitted using the monitored BPL.

In the second embodiment the PDCCH for a given UE is transmittednormally (for example every subframe) using the first BPL and inaddition the PDCCH is transmitted every Nth subframe using the secondBPL (the PDCCH from the two links may be transmitted on different OFDMsymbols when scheduled in the same subframe or slot so that it ispossible for the UE to switch to the UE RX beam corresponding to theright link).

Hence, if for example the PDCCH for the active BPL is scheduled on thefirst OFDM symbol and the PDCCH for the monitored BPL is scheduled onthe second OFDM symbol, the UE will use the first RX beam whenattempting to decode PDCCH candidates in the first OFDM symbol and thesecond RX beam when attempting to decode PDCCH candidates in the secondOFDM symbol. Stated differently, the UE will use the first spatial QCLparameter when attempting to decode PDCCH candidates in the first OFDMsymbol and the second spatial QCL parameter when attempting to decodePDCCH candidates in the second OFDM symbol. The UE will always try todecode the PDCCH candidates from the active BPL, and in one alternativeembodiment, if the decoding is successful the UE will not try to decodethe PDCCH candidates from the monitored BPL.

If the active BPL gets blocked such that the corresponding PDCCH cannotbe decoded by the UE, the UE can wait until the PDCCH is transmittedusing the monitored BPL and hopefully decode the PDCCH in this way. Inone embodiment the PDCCH from the monitored BPL contains a command thatswitch the active BPL to the monitored BPL directly. In this case, theUE shall start to monitor the search space candidates associated withthe monitored BPL directly, i.e. using the UE RX beam corresponding tothe monitored BPL.

As described above, the PDCCH from the active and monitored BPLs thatare in the same subframe must be scheduled on different OFDM symbols inthe same slot or subframe. The OFDM symbols containing the two PDCCHscan either be consecutive or have a time duration between them. Onebenefit with having a time duration between the two PDCCH is that the UEthen has time to evaluate if the PDCCH from the active BPL is properlydecoded before the PDCCH from the monitored BPL is received. Hence, incase the PDCCH corresponding to the active BPL is properly decoded theUE does not have to change UE RX beam corresponding to the monitored BPL(i.e., the RX beam of the monitored beam pair link) for the OFDM symbolcontaining the PDCCH for the monitored BPL. In this way it is possibleto also schedule data for the active BPL in this OFDM symbol in somecases (depending on antenna implementation at the TRP, antennaimplementation at the UE, scenario etc).

The PDCCH transmitted using the monitored BPL (e.g. the second spatialQCL parameter) can be transmitted every subframe or with a longer dutycycle compared to the PDCCH using the active BPL (first spatial QCLparameter). In some embodiments, for the subframes where no PDCCH istransmitted using the monitored BPL, only the first OFDM symbol is usedfor PDCCH (but in other embodiments more than one OFDM symbol may beused for PDCCH) and data can be scheduled for that second OFDM symbolinstead (because the start of the data symbols can be indicated in theDCI message).

In one embodiment the duty cycle for the PDCCH transmissions in themonitored BPL is configurable using higher layer signaling from TRP toUE, such as RRC signaling, depending on environment (for example howcommon blocking is) and can be either UE-specific or broadcasted. Itshould also be possible to turn it off completely.

FIG. 7 is a flow chart illustrating a process 700, according to someembodiments, that is performed by the TRP (which may have a firstcoverage area).

Process 700 may begin with step 702 in which the TRP uses a first BPL asan active BPL for the UE, wherein the first BPL comprises a first TXbeam and a first RX beam corresponding to the first TX beam (the firstBPL may have a second coverage area within the first coverage area).

In step 704, the TRP uses a second BPL as a monitored BPL for the UE,wherein the second BPL comprises a second TX beam and a second RX beamcorresponding to the second TX beam (the second BPL may have a thirdcoverage area that is within the first coverage area and that isdifferent than the second coverage area of the first BPL).

In step 706, while the first BPL is being used as the active BPL and thesecond BPL is being used as the monitored BPL the TRP transmits controlinformation (e.g., the PDCCH) to the UE using the first BPL (i.e., usingthe first TX beam).

In step 708, the TRP provides to the UE scheduling informationindicating a subframe in which the TRP may transmit control information(e.g., the PDCCH) to the UE using the second BPL (i.e., using the secondTX beam).

In some embodiments, process 700 further includes the TRP detecting thatthe first BPL has experienced a beam pair link failure (BPLF); and, as aresult of detecting that the first BPL has experienced a BPLF, the TRPtransmitting control information to the UE in the indicated subframeusing the second BPL.

In some embodiments, the control information transmitted to the UE inthe indicated subframe using the second BPL informs the UE that thesecond BPL is now an active BPL for the UE. In some embodiments, the UEis configured such that the UE will search a control area of theindicated subframe for control information transmitted by the TRP usingthe second BPL.

In some embodiments, the step of transmitting control information to theUE using the first BPL while the first BPL is being used as the activeBPL and the second BPL is being used as the monitored BPL comprisestransmitting control information to the UE using the first BPL in notmore than M of N consecutive subframes, wherein N is greater than 1 andM is less than or equal to N (in some embodiments M=N), and theindicated subframe is one of the N consecutive subframes.

In some embodiments, the scheduling information indicates L subframes(in some embodiments L=1) in which the TRP may transmit controlinformation to the UE using the second BPL, wherein L is greater than orequal to 1 and L is less than M, and each of the L subframes is one ofthe N consecutive subframes. In some embodiments, M=N−1 and L=1. In someembodiments, in one of the N consecutive subframes the TRP transmitscontrol information to the UE using the second BPL but does not transmitcontrol information to the UE using the first BPL.

FIG. 8 is a flow chart illustrating a process 800, according to someembodiments, that is performed by one or more transmission points (TRPs)communicating with a user equipment (UE) wherein the UE is monitoring acontrol channel search space of control channel message candidates (e.gPDCCH).

Process 800 may being with step 802 which consists of dividing resourcesfor the control channel search space for the UE into two parts, a firstpart and a second part, where the first part is associated with a firstQCL parameter and a second part is associated with a second QCLparameter. In step 804, for a transmission of a control channelcandidate to the UE, selecting the first or second part is selected. Instep 806, the control channel candidate is transmitted in controlchannel resources belonging to the selected part using the QCL parameterassociated with the selected part. In some embodiments, the first QCLparameter is related to an active BPL and the second QCL parameter isrelated to a monitored BPL, and the selection is based on informationthat the active BPL has experienced a BPLF (e.g., the active BPL has lowor no reception quality).

FIG. 9 is a flow chart illustrating a process 900, according to someembodiments, that is performed by a UE communicating with one or moretransmission points (TRPs), wherein the TRPs are configured to transmitinformation to the UE using a first BPL comprising a first TX beam and afirst RX beam corresponding to the first TX beam (the first BPL may havea second coverage area within the first coverage area).

Process 900 may begin in step 902 in which the UE uses the first RX beamcorresponding to the first TX beam to obtain control information (e.g.,PDCCH) transmitted by a TRP to the UE using the first BPL. In step 904,the UE obtains scheduling information indicating a subframe in which aTRP may transmit control information (e.g., the PDCCH) to the UE using asecond BPL comprising a second TX beam and a second RX beamcorresponding to the second TX beam (the second BPL may have a thirdcoverage area that is within the first coverage area but that isdifferent than the second coverage area of the first BPL). In step 906,the UE, as a result of receiving the scheduling information, uses thesecond RX beam corresponding to the second TX beam to search theindicated subframe for control information transmitted by a TRP to theUE using the second BPL. In some embodiments, a TRP transmits in thesubframe the control information to the UE using the second BPL in theevent that the TRP detects that the first BPL has experienced a beampair link failure (BPLF). In some embodiments, as a result of thesearch, the UE obtains control information transmitted to the UE usingthe second BPL, and the obtained control information informs the UE thathe second BPL is now an active BPL for the UE. In some embodiments, theindicated subframe is a subframe in which a TRP does not transmitcontrol information to the UE using the first BPL.

FIG. 10 is a flow chart illustrating a process 1000, according to someembodiments, that is performed by a UE communicating with one or moretransmission points (TRPs), wherein the TRPs are configured to transmitinformation to the UE using the first BPL. Process 1000 may begin instep 1002 in which the UE uses a first parameter corresponding to thefirst BPL to search a control area of a subframe for control information(e.g., PDCCH) transmitted by a TRP to the UE using the first BPL. Instep 1004, when the UE is unable to find the control informationtransmitted to the UE using the first BPL, the UE uses a secondparameter corresponding to the second BPL to search the control area ofthe subframe for control information (e.g., PDCCH) transmitted by a TRPto the UE using the second BPL.

FIG. 11 is a flow chart illustrating a process 1100, according to someembodiments, that is performed by a UE communicating with one or moretransmission points (TRPs), wherein the UE is monitoring a controlchannel search space of control channel message candidates (e.g PDCCH),wherein the control channel search space of control channel messagecandidates is divided into a least two parts, a first part and a secondpart. Process 1100 may being in step 1102 in which the UE uses a firstQCL parameter when receiving a control channel candidate of the firstsearch space part. In step 1104, the UE uses a second QCL parameter whenreceiving a control channel candidate of the second search space part.In some embodiments, the search space candidates of the two parts arereceived in two different OFDM symbols in one subframe. In someembodiments, the search space candidates of the two parts are receivedin two different subframes. In some embodiments, process 1100 furtherincludes the UE receiving configuration information using a higher layermessage (e.g., a layer 3 message, such as radio resource control (RRC)message), wherein the configuration information configures the divisionof the search space.

FIG. 12 is a flow chart illustrating a process 1200, according to someembodiments, that is performed by a system 1500 (see FIG. 15) comprisinga first transmission point (TRP) (e.g., TRP 550 as shown) forcommunicating with UE 501 and a second TRP 1502 for communicating withthe UE. Process 1200 may being in step 1202 in which the first TRP usesa first beam pair link (BPL) (denoted BPL #1) as an active BPL for theUE. In step 1204, the second TRP uses a second BPL (denoted BPL #2) as amonitored BPL for the UE. In step 1206, while the first BPL is beingused as the active BPL and the second BPL is being used as the monitoredBPL, the first TRP transmits control information (e.g., the PDCCH) tothe UE using the first BPL (i.e., using the TRP TX beam of the firstBPL). In step 1208, scheduling information is provided to the UE,wherein the scheduling information indicates a subframe in which thesecond TRP 1502 may transmit control information (e.g., the PDCCH) tothe UE using the second BPL (i.e., using the TRP TX beam of the secondBPL).

FIG. 13 is a block diagram of UE 501 according to some embodiments. Asshown in FIG. 13, the UE may comprise: a data processing system (DPS)1302, which may include one or more processors 1355 (e.g., a generalpurpose microprocessor and/or one or more other processors, such as anapplication specific integrated circuit (ASIC), field-programmable gatearrays (FPGAs), and the like); a radio transmitter 1305 and a radioreceiver 1306 coupled to an antenna 1322 for use in wirelesslycommunicating with a radio access network (RAN) node (e.g., a TRP); andlocal storage unit (a.k.a., “data storage system”) 1312, which mayinclude one or more non-volatile storage devices and/or one or morevolatile storage devices (e.g., random access memory (RAM)). Inembodiments where the UE includes a general purpose microprocessor, acomputer program product (CPP) 1341 may be provided. CPP 1341 includes acomputer readable medium (CRM) 1342 storing a computer program (CP) 1343comprising computer readable instructions (CRI) 1344. CRM 1342 may be anon-transitory computer readable medium, such as, but not limited, tomagnetic media (e.g., a hard disk), optical media (e.g., a DVD), memorydevices (e.g., random access memory, flash memory, etc.), and the like.In some embodiments, the CRI 1344 of computer program 1343 is configuredsuch that when executed by data processing system 1302, the CRI causesthe UE to perform steps described above (e.g., steps described abovewith reference to the flow charts). In other embodiments, the UE may beconfigured to perform steps described herein without the need for code.That is, for example, data processing system 1302 may consist merely ofone or more ASICs. Hence, the features of the embodiments describedherein may be implemented in hardware and/or software.

FIG. 14 is a block diagram of TRP 550 according to some embodiments. Asshown in FIG. 14, the TRP may comprise: a data processing system (DPS)1402, which may include one or more processors 1455 (e.g., a generalpurpose microprocessor and/or one or more other processors, such as anapplication specific integrated circuit (ASIC), field-programmable gatearrays (FPGAs), and the like); a radio transmitter 1405 and a radioreceiver 1406 coupled to an antenna 1422 for use in wirelesslycommunicating with a UE; and local storage unit (a.k.a., “data storagesystem”) 1412, which may include one or more non-volatile storagedevices and/or one or more volatile storage devices (e.g., random accessmemory (RAM)). In embodiments where the TRP includes a general purposemicroprocessor, a computer program product (CPP) 1441 may be provided.CPP 1441 includes a computer readable medium (CRM) 1442 storing acomputer program (CP) 1443 comprising computer readable instructions(CRI) 1444. CRM 1442 may be a non-transitory computer readable medium,such as, but not limited, to magnetic media (e.g., a hard disk), opticalmedia (e.g., a DVD), memory devices (e.g., random access memory, flashmemory, etc.), and the like. In some embodiments, the CRI 1444 ofcomputer program 1443 is configured such that when executed by dataprocessing system 1402, the CRI causes the TRP to perform stepsdescribed above (e.g., steps described above with reference to the flowcharts). In other embodiments, the TRP may be configured to performsteps described herein without the need for code. That is, for example,data processing system 1402 may consist merely of one or more ASICs.Hence, the features of the embodiments described herein may beimplemented in hardware and/or software.

Additional Embodiments

TRP Embodiments

1. A method performed by a transmission point (TRP) for communicatingwith a user equipment (UE), comprising: using a first beam pair link(BPL) as an active BPL for the UE, wherein the first BPL comprises afirst TX beam and a first RX beam corresponding to the first TX beam;using a second BPL as a monitored BPL for the UE, wherein the second BPLcomprises a second TX beam and a second RX beam corresponding to thesecond TX beam; while the first BPL is being used as the active BPL andthe second BPL is being used as the monitored BPL, transmitting controlinformation (e.g., the PDCCH) to the UE using the first BPL; andproviding to the UE scheduling information indicating a subframe inwhich the TRP may transmit control information (e.g., the PDCCH) to theUE using the second BPL.

2. The method of embodiment 1, further comprising: the TRP detectingthat the first BPL has experienced a beam pair link failure (BPLF); andas a result of detecting that the first BPL has experienced a BPLF, theTRP transmitting control information to the UE in the indicated subframeusing the second BPL.

3. The method of embodiment 2, wherein the control informationtransmitted to the UE in the indicated subframe using the second BPLinforms the UE that the second BPL is now an active BPL for the UE.

4. The method of embodiment 3, wherein the UE is configured such thatthe UE will search a control area of the indicated subframe for controlinformation transmitted by the TRP using the second BPL.

5. The method of any one of embodiments 1-4, wherein the step oftransmitting control information to the UE using the first BPL while thefirst BPL is being used as the active BPL and the second BPL is beingused as the monitored BPL comprises transmitting control information tothe UE using the first BPL in not more than M of N consecutivesubframes, wherein N is greater than 1 and M is less than or equal to N,and the indicated subframe is one of the N consecutive subframes.

6. The method of embodiment 5, wherein the scheduling informationindicates L subframes in which the TRP may transmit control informationto the UE using the second BPL, wherein L is greater than or equal to 1and L is less than M, and each of the L subframes is one of the Nconsecutive subframes.

7. The method of embodiment 6, wherein M=N−1 and L=1.

8. The method of embodiment 7, wherein in one of the N consecutivesubframes the TRP transmits control information to the UE using thesecond BPL but does not transmit control information to the UE using thefirst BPL.

9. The method of embodiment 6, wherein M=N and L=1.

10. A method performed by one or more transmission points (TRPs)communicating with a user equipment (UE) wherein the UE is monitoring acontrol channel search space of control channel message candidates (e.gPDCCH), the method comprising: dividing resources for the controlchannel search space for the UE into two parts, a first part and asecond part, where the first part is associated with a first QCLparameter and a second part is associated with a second QCL parameter;for a transmission of a control channel candidate to the UE, selectingthe first or second part; and transmitting the control channel candidatein control channel resources belonging to the selected part using theQCL parameter associated with the selected part.

11. The method of embodiment 10, where the first QCL parameter isrelated to an active BPL and the second QCL parameter is related to amonitored BPL.

12. The method of embodiment 11, where the selection is based oninformation that the active BPL has experienced a BPLF (e.g., the activeBPL has low or no reception quality).

13. A TRP comprising a transmitter, a receiver, a memory, and a dataprocessing system comprising one or more processors, wherein the TRP isconfigured to perform the method of any one of embodiments 1-12.

UE Side Embodiments

14. A method performed by a user equipment (UE) communicating with oneor more transmission points (TRPs), wherein the TRPs are configured totransmit information to the UE using a first beam pair link (BPL)comprising a first transmit (TX) beam and a first receive (RX) beamcorresponding to the first TX beam, the method comprising: the UE usingthe first RX beam corresponding to the first TX beam to obtain controlinformation (e.g., PDCCH) transmitted to the UE using the first BPL; theUE obtaining scheduling information indicating a subframe in which oneof the TRPs may transmit control information (e.g., the PDCCH) to the UEusing a second BPL comprising a second TX beam and a second RX beamcorresponding to the second TX beam; as a result of receiving thescheduling information, the UE using the second RX beam corresponding tothe second TX beam to search the indicated subframe for controlinformation transmitted to the UE using the second BPL.

15. The method of embodiment 14, wherein a TRP transmits in the subframethe control information to the UE using the second BPL in the event thatthe TRP detects that the first BPL has experienced a beam pair linkfailure (BPLF).

16. The method of embodiment 14 or 12, wherein, as a result of thesearch, the UE obtains control information transmitted to the UE usingthe second BPL, and the obtained control information informs the UE thathe second BPL is now an active BPL for the UE.

17. The method of any one of embodiments 14-13, wherein the indicatedsubframe is a subframe in which a TRP does not transmit controlinformation to the UE using the first BPL.

18. A method performed by a user equipment (UE) communicating with oneor more transmission points (TRPs), wherein the TRPs are configured totransmit information to the UE using a first beam pair link (BPL)comprising a first transmit (TX) beam and a first receive (RX) beamcorresponding to the first TX beam, the method comprising: the UE usinga first parameter corresponding to the first BPL to search a controlarea of a subframe for control information (e.g., PDCCH) transmitted bya TRP to the UE using the first BPL; when the UE is unable to find thecontrol information transmitted by the TRP to the UE using the firstBPL, the UE using a second parameter corresponding to a second BPL tosearch the control area of the subframe for control information (e.g.,PDCCH) transmitted by a TRP to the UE using the second BPL, wherein thesecond BPL comprises a second TX beam and a second RX beam correspondingto the second TX beam.

19. A method performed by a user equipment (UE) communicating with oneor more transmission points (TRPs), wherein the UE is monitoring acontrol channel search space of control channel message candidates (e.gPDCCH), wherein the control channel search space of control channelmessage candidates is divided into a least two parts, a first part and asecond part, the method comprising: the UE using a first QCL parameterwhen receiving a control channel candidate of the first search spacepart; and the UE using a second QCL parameter when receiving a controlchannel candidate of the second search space part.

20. The method of embodiment 19, wherein the search space candidates ofthe two parts are received in two different OFDM symbols in onesubframe.

21. The method of embodiment 19, wherein the search space candidates ofthe two parts are received in two different subframes.

22. The method of any one of embodiments 19-21, further comprising theUE receiving configuration information using a higher layer message(e.g., a layer 3 message, such as radio resource control (RRC) message),wherein the configuration information configures the division of thesearch space.

System Embodiments

23. A method performed by a system comprising a first transmission point(TRP) for communicating with a user equipment (UE) and a second TRP forcommunicating with the UE, comprising: the first TRP using a first beampair link (BPL) as an active BPL for the UE; the second TRP using asecond BPL as a monitored BPL for the UE; while the first BPL is beingused as the active BPL and the second BPL is being used as the monitoredBPL, the first TRP transmitting control information (e.g., the PDCCH) tothe UE using the first BPL; and providing to the UE schedulinginformation indicating a subframe in which the second TRP may transmitcontrol information (e.g., the PDCCH) to the UE using the second BPL.

24. The method of embodiment 23, further comprising: detecting that thefirst BPL has experienced a beam pair link failure (BPLF); as a resultof detecting that the first BPL has experienced a BPLF, the second TRPtransmitting control information to the UE in the indicated subframeusing the second BPL.

25. The method of embodiment 24, wherein the control informationtransmitted to the UE in the indicated subframe using the second BPLinforms the UE that the second BPL is now an active BPL for the UE.

26. The method of embodiment 25, wherein the UE is configured such thatthe UE will search a control area of the indicated subframe for controlinformation transmitted by the second TRP using the second BPL.

27. The method of any one of embodiments 23-26, wherein the step oftransmitting control information to the UE using the first BPL while thefirst BPL is being used as the active BPL and the second BPL is beingused as the monitored BPL comprises transmitting control information tothe UE using the first BPL in not more than M of N consecutivesubframes, wherein N is greater than 1 and M is less than or equal to N,and the indicated subframe is one of the N consecutive subframes.

28. The method of embodiment 27, wherein the scheduling informationindicates L subframes in which the second TRP may transmit controlinformation to the UE using the second BPL, wherein L is greater than orequal to 1 and L is less than M, and each of the L subframes is one ofthe N consecutive subframes.

29. The method of embodiment 28, wherein M=N−1 and L=1.

30. The method of embodiment 29, wherein in one of the N consecutivesubframes the second TRP transmits control information to the UE usingthe second BPL but the first TRP does not transmit control informationto the UE using the first BPL.

31. The method of embodiment 28, wherein M=N and L=1.

32. A UE comprising a transmitter, a receiver, a memory, and a dataprocessing system comprising one or more processors, wherein the TRP isconfigured to perform the method of any one of embodiments 14-22.

While various embodiments of the present disclosure are described herein(including the appendix), it should be understood that they have beenpresented by way of example only, and not limitation. Thus, the breadthand scope of the present disclosure should not be limited by any of theabove-described exemplary embodiments. Moreover, any combination of theabove-described elements in all possible variations thereof isencompassed by the disclosure unless otherwise indicated herein orotherwise clearly contradicted by context.

Additionally, while the processes described above and illustrated in thedrawings are shown as a sequence of steps, this was done solely for thesake of illustration. Accordingly, it is contemplated that some stepsmay be added, some steps may be omitted, the order of the steps may bere-arranged, and some steps may be performed in parallel.

The invention claimed is:
 1. A method performed by one or moretransmission points (TRPs) communicating with a user equipment (UE), themethod comprising: defining a first search space and a second searchspace, wherein a first transmit (TX) beam is associated with the firstsearch space and a second TX beam is associated with the second searchspace; for a transmission of a control channel candidate to the UE,selecting the first or second search space; and transmitting the controlchannel candidate in control channel resources belonging to the selectedsearch space using the TX beam associated with the selected searchspace, wherein the first search space is a first portion of a controlarea of a first subframe that has a data area that is separate from thecontrol area of the first subframe, and the second search space is asecond portion of the control area of said first subframe or the secondsearch space is a portion of a control area of a second subframe.
 2. Themethod of claim 1, where the first TX beam is related to a first BPL andthe second TX beam is related to a second BPL.
 3. The method of claim 2,where the selection is based on information that the first BPL hasexperienced a beam pair link failure.
 4. The method of claim 2, whereinthe second search space is a second portion of the control area of saidfirst subframe.
 5. The method of claim 4, wherein the first portion ofthe control area and the second portion of the control area overlap intime at least partially, or the first portion of the control area doesnot overlap in time with the second portion of the control area.
 6. Themethod of claim 2, wherein the first search space is the control area ofthe first subframe, and the second search space is the control area ofthe second subframe.
 7. A transmission point (TRP), the TRP comprising:a transmitter, a receiver, a memory, and a data processing systemcomprising one or more processors, wherein the TRP is configured toperform the method of claim
 1. 8. A method performed by a user equipment(UE) communicating with one or more transmission points (TRPs), themethod comprising: the UE using a first set of one or more quasico-location (QCL) parameters for receiving a control channel candidatein a first search space; and the UE using a second set of one or moreQCL parameters for receiving a control channel candidate in a secondsearch space, wherein, the first search space is a first portion of acontrol area of a first subframe that has a data area that is separatefrom the control area of the first subframe, and the second search spaceis a second portion of the control area of said first subframe or thesecond search space is a portion of a control area of a second subframe.9. The method of claim 8, wherein the second search space is a secondportion of the control area of said first subframe.
 10. The method ofclaim 9, wherein the first portion of the control area and the secondportion of the control area overlap in time at least partially, or thefirst portion of the control area does not overlap in time with thesecond portion of the control area.
 11. The method of claim 8, whereinthe first search space is the control area of the first subframe, andthe second search space is the control area of the second subframe. 12.The method of claim 8, wherein at least one of the QCL parameters ineach of the first and second sets of QCL parameters is a spatial QCLparameter.